Comment 5 for bug 388269

In the associated branch, I use this logic:

If the total walked-revisions exceeds 10,000, start at the current search tips, find their immediate children, and set that as the search graph.

I can easily extend this to something that walks the child graph until we hit something like 1k revs, or something else interesting-but-not-obscene.

In doing so, the time for initial discovery drops (against launchpad) from 5.5min down to 1m15s.

I still need a fair amount of polish and testing on the changes, but I think it shows promise.